The present invention relates to a band pass filter, and particularly, to a highly compact and easily fabricated band pass filter.
In recent years, marked advances in miniaturization of communication terminals, typically mobile phones, has been achieved thanks to miniaturization of the various components incorporated therein. One of the most important components incorporated in a communication terminal is a band pass filter.
As shown in xe2x80x9cA Novel TE10xcex4 Rectangular Waveguide Resonator and Its Bandpass Filter Applications (Proceedings of the Korea-Japan Microwave Workshop 2000, September 2000)xe2x80x9d, p. 88, FIG. 8, such a band pass filter is known wherein a plurality of TE mode half-wave (xcex/2) dielectric resonators are disposed on a printed circuit board at predetermined spacing. In the band pass filter described in this paper, the distances between the resonators (air gaps) work as so-called xe2x80x9cevanescent waveguidesxe2x80x9d to couple the adjacent resonators at a predetermined coupling constant.
As a need continues to be felt for still further miniaturization of the various communication terminals, further miniaturization of the band pass filter incorporated therein is also required.
In the band pass filter described above, however, the resonators must be mounted on the printed circuit board because they are coupled by the air gaps. The overall size of the band pass filter tends to be large because it is constituted of a plurality of independent components.
Further, in the band pass filter described above, the air gaps must be exactly adjusted to obtain desired characteristics. Even slight errors in the adjustment of the air gaps change the characteristics of the band pass filter markedly. Therefore, this makes the band pass filter described above very difficult to fabricate. The cost of the band pass filter is therefore high.
Thus, a compact and easily fabricated band pass filter is desired.
It is therefore an object of the present invention to provide a compact and easily fabricated band pass filter.
The above and other objects of the present invention can be accomplished by a band pass filter comprising: a first half-wave (xcex/2) resonator having a first open end on which an input terminal is formed and a second open end opposite to the first open end, a second half-wave (xcex/2) resonator having a third open end on which an output terminal is formed and a fourth open end opposite to the third open end, and an evanescent waveguide interposed between the second open end of the first resonator and the fourth open end of the second resonator, the first half-wave (xcex/2) resonator, the second half-wave (xcex/2) resonator, and the evanescent waveguide being a single unit.
According to this aspect of the present invention, because the first half-wave (xcex/2) resonator, the second half-wave (xcex/2) resonator, and the evanescent waveguide are a single unit, they do not have to be mounted on a printed circuit board to form an air gap. Therefore, the overall size of the band pass filter can be reduced and fabrication of the band pass filter is simplified.
In a preferred aspect of the present invention, the first half-wave (xcex/2) resonator, the second half-wave (xcex/2) resonator, and the evanescent waveguide are made of a single dielectric unit.
In a further preferred aspect of the present invention, an overall dimension of the band pass filter is a substantially rectangular prismatic shape.
In a further preferred aspect of the present invention, a passing band of the band pass filter is not less than 5 GHz.
The above and other objects of the present invention can be also accomplished by a band pass filter comprising:
first and second dielectric blocks each of which has a top surface, a bottom surface, first and second side surfaces opposite to each other, and third and fourth side surfaces opposite to each other;
a third dielectric block in contact with the first side surface of the first dielectric block and the first side surface of the second dielectric block;
metal plates formed on the top surfaces, the bottom surfaces, the third side surfaces, and the fourth side surfaces of the first and second dielectric blocks;
a first electrode formed on the second side surface of the first dielectric block; and
a second electrode formed on the second side surface of the second dielectric block.
Also according to this aspect of the present invention, an air gap does not have to be formed by mounting components on a printed circuit board. Therefore, the overall size of the band pass filter can be miniaturized and fabrication of the band pass filter is simplified.
In a preferred aspect of the present invention, the first dielectric block and the second dielectric block have the same dimensions.
In a further preferred aspect of the present invention, the third dielectric block has a first side surface in contact with the first side surface of the first dielectric block, a second side surface in contact with the first side surface of the second dielectric block, a third side surface parallel to the third side surface of the first dielectric block, a fourth side surface parallel to the fourth side surface of the first dielectric block, a top surface parallel to the top surface of the first dielectric block, and a bottom surface parallel to the bottom surface of the first dielectric block on which a metal plate is formed.
In a further preferred aspect of the present invention, the bottom surfaces of the first to third dielectric blocks are coplanar.
In a further preferred aspect of the present invention, the top surfaces of the first to third dielectric blocks are coplanar.
In a further preferred aspect of the present invention, the members of at least one pair of surfaces among a first pair consisting of the top surfaces of the first and third dielectric blocks, a second pair consisting of the third surfaces of the first and third dielectric blocks, and a third pair consisting of the fourth surfaces of the first and third dielectric blocks fall in different planes.
In a further preferred aspect of the present invention, the first dielectric block and the metal plates formed on the top surface, bottom surface, second side surface, and third side surface thereof constitute a first half-wave (xcex/2) dielectric resonator, the second dielectric block and the metal plates formed on the top surface, bottom surface, second side surface, and third side surface thereof constitute a second half-wave (xcex/2) dielectric resonator, and the third dielectric block constitutes an evanescent waveguide.
The above and other objects of the present invention can be also accomplished by a band pass filter comprising: a plurality of half-wave (xcex/2) dielectric resonators and at least one evanescent waveguide interposed between adjacent half-wave (xcex/2) dielectric resonators, the half-wave (xcex/2) dielectric resonators and the evanescent waveguide being made of a single dielectric unit.
Also, according to this aspect of the present invention, an air gap does not have to be formed by mounting components on a printed circuit board. Therefore, the overall size of the band pass filter can be miniaturized and fabrication of the band pass filter is simplified.
In a preferred aspect of the present invention, an overall dimension of the band pass filter is a substantially rectangular prismatic shape.
In another preferred aspect of the present invention, at least one slit is formed in the dielectric block at a portion thereof acting as the evanescent waveguide.
The above and other objects of the present invention can be also accomplished by a band pass filter comprising: a dielectric block of substantially rectangular prismatic shape constituted of a first portion lying between a first cross-section of the dielectric block and a second cross-section of the dielectric block substantially parallel to first cross-section and second and third portions divided by the first portion and metal plates formed on the surfaces of the dielectric block, thereby enabling the first portion of the dielectric block and the metal plates formed thereon to act as an evanescent waveguide, the second portion of the dielectric block and the metal plates formed thereon to act as a first resonator, and the third portion of the dielectric block and the metal plates formed thereon to act as a second resonator, the metal plates being formed on, among the surfaces of the second and third portions of the dielectric block, each surface which is substantially perpendicular to the cross-sections.
According to this aspect of the present invention, since the band pass filter is constituted of the dielectric block of rectangular prismatic shape, the mechanical strength is extremely high and low in cost.
In a preferred aspect of the present invention, the metal plates further include a first exciting electrode formed on, among the surfaces of the second portion of the dielectric block, a surface which is substantially parallel to the cross-sections and a second exciting electrode formed on, among the surfaces of the third portion of the dielectric block, a surface which is substantially parallel to the cross-sections.